JPH089116A - Image reader - Google Patents

Abstract

PURPOSE:To provide a shading correction means in which reduction in the throughput is reduced in the image reader having the placing original read mode and the carrying original read mode. CONSTITUTION:An image of an original read in the 1st original read mode to read a placed original and in the 2nd original read mode to read a carrying original is subjected to photoelectric conversion from an optical signal into an electric signal by using a photoelectric conversion element 8. Shading is corrected in the 1st original read mode by using a shading waveform obtained by reading a 1st white reference board 18 and shading is corrected in the 2nd original read mode by using a shading waveform obtained by reading the 1st white reference board 18 and correcting the waveform based on data obtained through the reading of a 2nd white reference patch 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus for reading an original image using a photoelectric conversion element, converting an optical signal into an electric signal, and then obtaining a digitized image signal using an A / D converter or the like. In particular, the present invention relates to shading correction in an image reading apparatus having two modes: a placed original reading mode for reading an original stacked on an original platen glass and a conveyed original reading mode for reading an original being conveyed.

[0002]

2. Description of the Related Art FIG. 5 shows an example of the configuration of a conventional image reading apparatus which is used both for reading a stacked original document and for reading a conveyed original document.

The main part of this type of image reading apparatus is the original document 4.
An original reading optical system 1 for scanning and reading a sheet, an automatic original feeder 2 for feeding a sheet original to an original reading position, and an original table glass 3 on which an original such as a book is placed.

The document reading optical system 1 comprises an exposure lamp 5 for illuminating a document, a reflecting mirror 6 and an image forming lens 7,
The image processing system comprises a photoelectric conversion element 8, an amplifier 9 and an analog-digital converter (A / D converter) 10. The exposure lamp 5 and the reflection mirror 6 are configured to be movable between positions A and B in parallel with the platen glass 3 by a driving source (not shown), and optically scan the placed document 4. Further, the exposure lamp 5 and the reflection mirror 6 are also configured to be movable to the position C by a driving source (not shown).

The automatic document feeder 2 includes a document tray 11, a document insertion port 12, a document separating section 13, pinch rollers 14a and 14b for document transportation, a reading roller 14 and a document ejection port 1.
5 and a discharged document tray 16. In the automatic document feeder 2, the sheet-shaped originals 4 each having the leading end inserted into the original insertion port 12 and placed on the original tray 11 are fed out one by one by the rollers of the original separating section 13 and in opposite directions. After being conveyed by the pinch rollers 14a / b that rotate to the left and fed to the reading roller 14 provided with a gap above the conveyed document reading surface 17, the document is ejected to the ejected document tray 16.

The two original reading modes will be described below.

[Loaded original reading mode] Original platen glass 3
A document 4 such as a book placed on the document is illuminated by an exposure lamp 5, and the optical image of the document thus illuminated is reflected by a reflection mirror 6.
An image is formed on the photoelectric conversion element 8 via the image forming lens 7 and an optical signal is converted into an electric signal. The exposure lamp 5 and the reflection mirror 6 are moved from a position A to a position B by a driving source (not shown) to read and scan the stacked document surface line by line.

[Transported Document Reading Mode] Document Inserting Port 12
The originals 4 inserted from the are passed through the original separating section 13 by a drive source (not shown), and are separated into a plurality of sheets one by one, and are sent toward the reading roller 14. The reading roller 14 feeds a document by pressure contact with the pinch rollers 14a and 14b and feeds the document to the document discharge port 15. Reading roller 14
The reading roller 14 on the original reading surface 17 provided opposite to
The surface opposite to is on the same plane as the platen glass 3 and has the same glass thickness. Further, a small gap is provided between the reading roller 14 and the document reading surface 17 so that the document can be fed. When scanning the transported original,
The scanning optical system 1 moves to the position C and stops there,
The original conveyed by the conveying system 2 is read.

By the way, in this type of image reading apparatus, it is necessary to define an absolute white level. This is the output of the photoelectric conversion element 8 when a white original is read, and one line in the main scanning direction is read, and is usually called a shading waveform. Since the output of the exposure lamp 5 changes depending on the environmental temperature, the lighting time, or the cumulative usage time, the shading waveform also changes according to these changes. Further, the luminous intensity also changes in the longitudinal direction (main scanning direction) of the lamp. When reading a document illuminated by such an exposure lamp, the shading waveform obtained by reading the white surface is regarded as the maximum output value, and a correction called shading correction is performed to correct the read image signal using the shading waveform. To obtain a proper image signal.

In order to perform this shading correction, the image reading apparatus has a white reference plate 1 having a reference white reflection surface.
8 is provided, and the white reference plate 18 is read each time the original is read, and the result is stored as a shading waveform in the storage means provided in the image signal processing means. As shown in FIGS. 5 and 6, the white reference plate 18 is attached to the reading start end (position A) of the platen glass 3.

When reading the stacked originals, the white reference plate 18 is read for the width of the original at position A in FIG. 6 before the reading is started, and the shading waveform is stored in the storage means. Subsequently, the scanning optical system moves in the direction of the position B to scan the original surface, and the original 4 placed on the original table glass 3 is scanned.
To the end. When reading the conveyed original, the optical system 1 first scans the white reference surface 18 at the position A to read the shading waveform, then moves to the position C, and reads the original sent from the automatic paper feeder. .

[0012]

As described above, the shading waveform changes with the lighting time of the exposure lamp 5. Therefore, it is desirable to reread the white reference plate 18 and update the shading waveform every time one page of the original is read in order to obtain a good quality image. However, at the time of reading the conveyed document, the optical system 1 must be returned to the position A and the shading waveform must be read again every time one page is read, which causes a problem that the throughput of the system decreases.

In order to solve this problem, as shown in FIG. 7, in the method disclosed in Japanese Patent Laid-Open No. 63-287160, a white reference plate corresponding to the transport original reading mode and the stacked original reading mode is used. In the conveyed document reading mode, in the conveyed document reading mode, the reduction of throughput is solved by reading the conveyed document reading white reference plate 19 arranged at a position facing the conveyed document reading position for each document conveyance. ing.
However, in this means, the white reference plate 19 for reading the conveyed original must be provided on the conveyed original reading surface 17 through a gap through which the original can pass without any trouble, and therefore the reading optical length differs for each reading mode. In addition to the problem that the optimum image forming position cannot be obtained, in the transported original reading mode, the original directly contacts the white reference plate 19, so the white reference plate 1
There is a problem that foreign matter such as paper dust adheres to the sheet 9, so that a correct shading waveform cannot be obtained, and as a result, a defect such as a black streak or a white streak occurs in the read image after the shading correction.

It has also been proposed to make the reading roller 14 shown in FIG. 5 white and use it as a white reference plate for the conveyance original reading mode. In this case, since the reading roller 14 is located very close to the platen glass 3, it is unlikely that the image forming positions are different in both modes, but the density of the reading roller 14 and the white reference plate 18 for the stacked original reading mode is different. If the (whiteness) and the spectral distribution are not perfectly matched, there is a problem that the original reading density differs depending on the mode.

In the means disclosed in Japanese Patent Laid-Open No. 64-19865, the white reference plate for the loaded original reading mode and the reading roller are read under the same conditions (reading width, elapsed time after the exposure lamp is turned on, etc.). Then, the output ratio r is calculated (white reference plate: reading roller = 1: r), and this ratio is set in advance as a shading correction coefficient. The reading roller surface is read before reaching, and the output ratio r is added to the waveform data.
The reading characteristics are matched in each mode by multiplying by. However, even with this means, since the reading roller directly touches the document, the problem caused by the above-mentioned adhesion of foreign matter such as paper dust remains.

[0016]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an image reading apparatus including a white reference plate for a loaded document reading mode provided on a document stacking table and a transported document reading position. A white reference patch for the conveyance original reading mode is provided on the original loading table outside the original reading area. With this configuration, in the loaded document reading mode, shading correction is performed by the shading waveform obtained by reading the white reference plate for the loaded document reading mode, and in the conveyed document reading mode, the white reference plate for the loaded document reading mode is temporarily read and shaded. Corresponds to the read data of the white reference patch for document scanning and the position and size of the patch stored in the memory for waveform storage after the optical system has been stored in the memory for waveform recording and moved to the document scanning position for document transportation. The output ratio r is obtained from the data for each document conveyance, and the output ratio r is added to the read data of the memory for shading waveform storage.
Shading correction is performed using the shading correction data multiplied by.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an image reading apparatus for both loading document reading and conveying document reading according to the present invention will be described with reference to FIGS. 1 and 2. The main part of the image reading apparatus of the present invention is the original 4
An original reading optical system 1 for scanning and reading a document, an automatic document feeder 2 for feeding a sheet original to a document reading position, and an original table glass 3 on which an original such as a book is placed. Further, the image reading apparatus of the present invention is characterized by including a placed original reading white reference plate 18 and a conveyed original reading white reference patch 30.

The document reading optical system 1 comprises an exposure lamp 5 for irradiating a document, a reflection mirror 6 and an image forming lens 7. The image signal processing system includes a photoelectric conversion element 8, an amplifier 9 and an A
/ D converter 10, shading correction circuit 20, shading waveform storage memory 21 for storing shading waveforms, image processing unit 22, correction memory 23 for storing correction signals, and images for reproducing images in the form of hard copy It comprises a forming unit 24 and a CPU 25 for measuring the operation of the image signal processing system. The exposure lamp 5 and the reflection mirror 6 are configured to be movable between positions A and B in parallel with the platen glass 3 by a driving source (not shown).
Is optically scanned. Further, the exposure lamp 5 and the reflection mirror 6
Is also movable to the position C by a drive source (not shown).

The automatic document feeder 2 includes a document tray 11, a document insertion slot 12, a document separating section 13, pinch rollers 14a and 14b for transporting a document, a reading roller 14, and a document discharge port 1.
5 and a discharged document tray 16. In the automatic document feeder 2, the sheet-shaped originals 4 each having the leading end inserted into the original insertion port 12 and placed on the original tray 11 are fed out one by one by the rollers of the original separating section 13 and in opposite directions. After being conveyed by the pinch rollers 14a / b that rotate to the left and fed to the reading roller 14 provided with a gap above the conveyed original reading surface 17, the discharged original tray 1
It is discharged to 6.

As shown in FIG. 2, the mounted original reading white reference plate 18 has substantially the same structure as the conventional white reference plate,
It differs from the conventional one in that it extends outside the maximum reading width of the original. Further, the white reference patch 30 for reading the conveyed document is characterized in that it is provided at the conveyed document reading position C and is installed outside the maximum document reading width.

Each reading mode in the present invention will be described below. Usually after one continuous use,
Alternatively, the scanning optical system is in position A when the power is turned on.

[Loaded Original Reading Mode] Similar to the conventional example, after scanning the shading waveform from the white reference plate 18 for stacked original reading mode and storing it in the memory 21 for storing the shading waveform, the scanning optical system 1 is directed to the position B. Scan the document 4 that is moved and placed on the platen glass 3,
The obtained image information is converted into an electric signal by the photoelectric conversion element 8 and the image information for each line is read. The read image information for each line is stored in the shading waveform storage memory 21.
The shading waveform information stored in (1) is corrected, and the image processing unit 22 processes it into information suitable for image formation in the image forming unit 24.

[Conveyed Original Reading Mode] When the white reference plate 18 for the stacked original reading mode is at position A and when it is assumed that the white reference plate 18 for the stacked original is at the conveyed original reading position C, the reading width and the light source are turned on. Under the condition that the time is the same, both outputs of the white reference plate are the same. Therefore, if there is a white reference patch 30 of the same quality as the white reference plate 18 in a part of the conveyed document reading position C, the data obtained by reading the white reference patch 30 and the same position in the white reference plate 18 after an arbitrary lighting time has elapsed. It is possible to obtain the rate of change in the shading waveform based on the elapsed lighting time, that is, the correction rate, by using the read data.

Further, even when the time elapsed after the light source is turned on at the time of reading at the position A is different from that at the time of reading at the position B, the shading waveform output becomes a similar system as shown in FIG. If the output ratio is set to 1: r, the ratio itself is the same at every pixel position in the shading waveform. Therefore, if there is a white reference of the same quality as the white reference plate 18 in a part of the conveyed document reading position C, that reading is performed. The ratio r can be obtained from the data and the read data at the same position in the white reference plate 18 at the position A.

In the case of the conveyance original reading mode, before the scanning optical system 1 moves to the conveyance original reading position C, the stacked original reading mode white reference plate 18 is read at the position A and stored in the shading waveform storage memory 21. Store it. The stacked original reading mode white reference plate 18 has a correction reading range 18-1 that exceeds the original reading range, and the shading waveform storage memory 21 also stores the read data of the correction reading range. Remembered

Next, the scanning optical system 1 moves to the position C,
The scanner is in the standby state for reading the conveyed document. Immediately before the document is conveyed by the automatic document feeder 2, the conveyed document reading white reference patch 30 is read at the same position, and the average value X1 is calculated from the read image data. Next, in the shading waveform storage memory 21, an average value X2 is similarly calculated from the image data of the address corresponding to the position and size of the conveyed document reading white reference patch (reading data of the correction reading range). , X1 / X2, the output ratio r is obtained. When the shading waveform data output from the shading waveform storage memory 21 is multiplied by this ratio r, correction data that matches the shading waveform data when the white reference plate 18 is read at the conveyed document reading position C is obtained. The image data read at the conveyed document reading position C is corrected using this correction data.

When processing a plurality of originals 4, the automatic original feeder 2 separates the originals one by one, and it is necessary to detect page breaks in image processing. It is equipped with a mechanism for feeding a sheet with a gap provided between the page and the leading edge. Therefore, after the reading of a certain page is completed, the white reference patch 30 can be read until the next page reaches the reading position, and the ratio r can be updated for each page. The shading waveform itself is obtained by reading the white reference plate 18 for the loaded document reading mode, and white reference stains due to document conveyance do not occur. Therefore, stable shading correction can be performed at all times. Further, even in the conveyed document reading mode, it is possible to quickly and accurately follow the temporal change in the brightness of the light source 5.

FIG. 1 is a block diagram showing a circuit configuration example of an image reading apparatus according to the present invention. The optical image of the document optically scanned by the exposure lamp 5 and the reflection mirror 6 is
An image is formed on the photoelectric conversion element 8 via the reflection mirror 6 and the lens 7, and an optical signal is converted into an electric signal. This electric signal is amplified to a predetermined size by the amplifier 9,
The analog signal is converted into an n-bit digital signal in the / D converter 10 and then sent to the shading correction circuit 20. The shading waveform of the white reference 18 is now stored in the shading waveform storage memory 21.

Image data at the time of reading an original is obtained by using the shading waveform read from the shading waveform storage memory 21 in the shading correction circuit 20.
Shading is corrected. The image after shading correction is further subjected to image processing such as filtering and reduction / enlargement in the image processing unit 22, and then sent to the image forming unit 24 and printed on a sheet. The correction memory 23 is a line memory in which data of processing such as filtering and reduction / enlargement is stored. Further, the CPU 25 controls the scanning optical system 1, the exposure lamp 5, the image processing unit 22, and the like as a whole of the reading device.

The shading correction circuit 2 will be described with reference to FIG.
The operation of 0 will be described. The shading correction circuit 20
A multiplication circuit 201 for multiplying the shading waveform data read from the shading waveform storage memory 21 by a predetermined coefficient, a register 202 for setting the coefficient,
The shading correction calculation unit 203 is configured to perform shading correction calculation using the image data obtained by reading the original and the image data from the multiplication circuit 201.

[Shading Correction in Loaded Original Reading Mode] The white reference plate 18 is read prior to the reading operation of the loaded originals, and the shading waveform for one line is stored in the shading waveform storage memory 21. The shading waveform data read from the shading waveform storage memory 21 at the time of reading the loaded document is used as the multiplication circuit 201.
Is sent to the shading correction calculation unit 203 via. The coefficient 1.0 is set in the coefficient setting register 202, and the shading waveform data read from the shading waveform storage memory 21 is output as it is. The shading correction calculation unit 203 performs shading correction using the image data obtained by reading the document and the shading waveform data corresponding to the pixel positions thereof. If the image data is 8 bits, the correction calculation formula is (25
5 ÷ shading waveform data) × document reading data.

[Shading Correction in Conveyance Original Reading Mode] The scanning optical system 1 reads the stacked original reading white reference plate 18 at the position A and includes a correction reading range 18-1.
The shading waveform data for the lines is stored in the shading waveform storage memory 21. Next, the scanning optical system 1 moves to the conveyed document reading position C, and the automatic document feeder 2
Immediately before the original 4 is conveyed to the conveyed original reading position C, the conveyed original reading white reference patch 30 is read at the same position and the read data (white reference patch read data) is stored in the correction memory 23. The CPU 25 accesses the correction memory 23 and calculates the average value X1 from the white reference patch read data. Next, the CPU 25 controls the white reference patch 3 stored in the shading waveform storage memory 21.
Similarly, the average value X2 is calculated using the image data of the address corresponding to the position 0 (correction range), the output ratio r is calculated from X1 / X2, and the ratio r is set in the coefficient setting register 202.

The shading waveform data read from the shading waveform storage memory 21 at the time of reading the conveyed original is sent to the shading correction calculation unit 203 via the multiplication circuit 201, but the ratio r is stored in the coefficient setting register 202. Is set, and the shading waveform data is multiplied by r and sent to the shading correction calculation unit 203. This ratio r is updated for each page as described above. The correction calculation formula is the same as that in the loaded document reading mode.

As described above, in this embodiment, the white reference patch 30 for reading the conveyed original is provided outside the original reading area of the conveyed original reading position C, but the white reference is used for the reading roller 14 described in the conventional section. The present invention can be practiced by using a product whose color is white and whose length is extended to the range of the white reference patch 30. In this case, the output ratio r is obtained from the read data of the white reference plate 18 and the white reference patch position of the reading roller 14 each time the document is conveyed by the automatic document feeder, and the ratio r is set as a coefficient, as in the above embodiment. It may be set in the register 202.

Since the reading roller 14 has a problem of dust and dirt caused by document transportation as described in the section of the prior art, the CPU 25 uses the correction memory 2 as a countermeasure against the problem.
When the white base patch read data of the reading roller 14 stored in No. 3 is accessed, the size of the accessed data is compared with the size of the data before and after the accessed data, and if the result is a certain ratio or more, the pixel is selected. By removing the abnormal pixels from the calculation data and obtaining the average value X1, the influence of dust and dirt is prevented.

[0036]

As described above, according to the present invention, in the transported original reading mode, the white reference plate 18 for the stacked original reading mode is used.
Storing the shading waveform data obtained by once reading in the memory for storing the shading waveform, and reading the white reference patch for reading the conveyed original at the conveyed original reading position,
An output ratio r is obtained for each document conveyance from the read data and data corresponding to the position and size of the patch in the shading waveform storage memory, and the read data in the shading waveform storage memory is multiplied by the output ratio r. Since the shading correction is performed using the data, the throughput of the system is not reduced, and the read data of the white reference plate 18 for the stacked document reading mode is used as the basic shading waveform data. It was possible to solve the problem of adhesion of paper dust and the like caused by the original directly touching the white reference plate.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an image processing apparatus according to the present invention.

FIG. 2 is a top view showing a configuration of a document placing table of the image processing apparatus according to the present invention.

FIG. 3 is a diagram showing a temporal change of a shading waveform.

FIG. 4 is a detailed block diagram of a shading correction circuit of the image processing apparatus according to the present invention.

FIG. 5 is a block diagram showing a configuration of an image processing apparatus according to a conventional technique.

FIG. 6 is a top view showing a configuration of a document placing table of an image processing apparatus according to a conventional technique.

FIG. 7 is a block diagram showing the configuration of another example of an image processing apparatus according to the related art.

[Explanation of symbols]

1 original reading optical system, 2 automatic document feeder, 4
Documents, 5 exposure lamps, 6 reflection mirrors, 7 imaging lenses, 8 photoelectric conversion elements, 9 amplifiers, 10
Analog-digital converter, 11 manuscript tray,
12 document insertion port, 13 document separating section, 14 reading roller, 15 document ejection port, 16 ejection document tray, 17 conveyance document reading surface, 18 white reference plate for reading placed document, 19 white reference plate for conveyance document reading, 20
Shading correction circuit, 21 shading waveform storage memory, 22 image processing unit, 23 correction memory, 25 CPU, 30 transport reference white reference patch, 201 multiplication circuit, 202 coefficient register, 2
03 Shading correction calculator.

Claims (4)

[Claims] 1. A first original reading mode in which an optical system scans an original placed on an original loading table by an optical system to read an original image, and an optical system stops at a specific position while the original is conveyed by an original conveying unit. And a second original reading mode for reading the original image in such a state that the photoelectric conversion device converts the optical image of the original image read in both modes into an electric signal. The first white reference plate serving as the white reference in the original reading mode and the second white reference patch serving as the white reference in the second original reading mode are provided, and the shading correction in the first original reading mode and the first white reference patch Shading correction in the original 2 reading mode is
The image reading apparatus is characterized in that both are performed based on a shading waveform obtained by reading a common white reference plate. 2. The shading correction in the first original reading mode is performed using a shading waveform obtained by reading the first white reference plate, and the shading correction in the second original reading mode is performed using the first white reference. The image reading apparatus according to claim 1, wherein the shading waveform obtained by reading the plate is corrected using a shading waveform corrected by a predetermined constant based on data obtained by reading the second white reference patch. 3. The image reading apparatus according to claim 2, wherein the predetermined constant is obtained as a result of calculating read data of the first white reference plate and read data of the second white reference patch. 4. The second white reference patch is provided outside the document reading area in the main scanning direction at the document reading position in the second document reading mode. Image reading device.